Constant pressure output control for variable displacement pump



A nl 21, 1959 N. B. NEWTON 2,8

CONSTANT PRESSURE OUTPUT CONTROL FOR VARIABLE DISPLACEMENT PUMP mmamwmqm Lmfiao 135a Filed Oct. 19, 1954 HIV/170A 1371/70 dW/Id INVENTOR ORMAN B. NEWTON MwwwNQ F a 3528 mkomkw m di l oSSo. A c N F33 r IL U\u mkoEw. 25 1331 P3 A TTORNEY United States Patent CONSTANT PRESSURE OUTPUT CONTROL FOR VARIABLE DISPLACEMENT PUMP Norman B. Newton, South Glastonbury, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application October 19, 1954, Serial No. 463,133

7 Claims. (Cl. 121-41) The invention relates to hydraulic systems but more specifically to pressure control mechanism for such systems.

It is an object of this invention to provide a pressure control mechanism which would control the pump stroke in a system supplied by a variable displacement pump or would control the opening of a bypass valve in a system supplied by any other source of pressure so as to maintain a constant pressure at any given output within the system capacity.

It is another object of this invention to provide a control system for a variable displacement pump which system provides for rapidly increasing the pump pressure at maximum capacity and sharply decreasing volumetric output when the desired controlled output pressure is reached.

It is a further object of this invention to provide a control system of the type described including a spring pressed valve which has a follow-up system for maintaining the compression of the spring constant at all times.

These and other objects will become readily apparent from the following detailed description of the drawing in which:

Fig. 1 is a schematicillustration of a pump having a displacement control valve according to this invention.

Fig. 2 is an enlarged detailed cross section view of the main control valve and Fig. 3 graphically illustrates the pump operation with and without a spring tensioning follow-up device.

Referring to Fig. 1 a pump is schematically illustrated as having a stroke control schematically shown at 12 and a control valve 14 for regulating the stroke control system. The pump 10 may be of the type shown in Patent No. 2,673,526 and the stroke control mechanism generally may be of the type disclosed in that patent. The control valve 14 normally would be located within the pump casing and would be surrounded by drain oil within the casing. However, the valve is illustrated schematically in Fig. 1 in order to provide a clear picture of the flow lines.

Referring to Fig. 2 the valve generally indicated at 14 has an outer casing 20 having an inlet opening 22. Fluid under pressure from the pump outlet is conducted internally of the casing 20 through the passage 22 whereit can act on the right hand end of a valve stem 24. The fluid under pressure will act on an area equivalent to the cross sectional area of the valve stem 24. The valve stem 24 is surrounded by an annular member 26 which is an extension of a servo piston 28. The piston 28 is slidable axially within a cylinder 30. The valve 24 carries a disc like member 31 which acts to damp movement of the valve. The amount of damping will depend upon the amount of clearance at the periphery of the disc or will depend upon the size the slots formed in the outer rim of the disc.

The annular extension 26 which is formed integrally with the piston 28 includes at least one set of grooves 32 and 34 which communicate with drilled passages 36 and 38.

The righthand end of the valve stem 24 includes an abutment 40 adjustably fixed thereto and is engaged by one end of a compression spring 42. The other end of the spring 42 is engaged by an abutment 44 carried by an annular sleeve 46 which surrounds the annular guide member 48. The annular guide member 48 is an axial extension of cylinder 30. The sleeve 46 at its righthand end has an inwardly extending flange 50 which engages the righthand end of the annular member 26. As mentioned previously, the member 26 is integral with and movable with the servo piston 28. When the pump outlet pressure reaches a predetermined value, valve stem 24 will be moved toward the left from the position shown against the force of the spring 42. Movement of valve stem 24 toward the left will move the land 56 toward the left, thus permitting high pressure fluid to flow via the groove 34 through the ports 38 and 36, then along the groove 32 to the chamber 58 on the righthand side of the piston 28. This will cause the piston to move toward the left. Extending left from the piston 28 is a hollow actuating rod 62 which is in turn connected to a yoke 64 which may suitably engage the eccentric track ring of the type shown for example in Patent No. 2,673,526. Movement of the track ring varies the stroke and capacity of the pump.

Movement of the servo piston 28 to the left causes fluid to drain from the chamber 70 on the lefthand side of the piston 28 through a groove 72 and then through passage 74 to the port 76 in the valve stem 24. The port 76 is connected to a hollow drain passage 78 which leads to a passage 80 and then out the drain port 82 adjacent the lefthand end of the valve casing. It will be apparent that a reduction of pressure from the pump outlet would permit the spring 42 to move the valve stem 24 toward the right, thereby permitting high pressure fluid to flow through the passage 74 in the groove 72 with the chamber 70 on the lefthand side of piston 28 thereby moving the piston to the right. With a construction of the type described herein, the follow-up sleeve 46 is provided which in turn moves in unison with the servo piston 28. The compression in the spring 42 remains substantially constant independent of the position of the servo piston 28. Hence I obtain an operating curve similar to the curve A shown in Fig. 3. Thus it is possible to rapidly arrive at the desired pump outlet pressure before decreasing pump displacement.

Without the sleeve 46 the compression of the spring 42 would be dependent upon the position of the servo piston 28 and hence its compression would vary so that an operating curve such as B in Fig. 3 would obtain. It can be seen that the volumetric outlet of the pump would be reduced slowly before reaching the maximum desired pump outlet pressure. There may be some installations where it would be desirable to obtain a curve such as B in certain instances. It is thus possible to conveniently convert the particular valve shown from a constant pressure control to a control that produces a curve such as B shown in Fig. 3.

In any event with the construction shown, maximum volumetric output of the pump is assured until just before the desired output pressure is reached at which time the control valve will immediately reduce pump displacement and regulate at the desired pressure.

With a control for a variable displacement hydraulic pump of the type described, a compact mechanism as well as a rugged and accurate structure has been provided.

Although only one embodiment of this invention has been shown and described herein, it will be apparent that various changes and modifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

What it is desired to'obtainby Letters 'Patent is:

1. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing and a cooperating cylinder, said cylinder being fixed to said casing, passage means connecting said casing with said source, a drain, a valve movable relative to said casing having one end exposed to fluid pressure from said passage means and urging said valve in a direction to connect one side of said piston with pressure from said source, a spring urging said valve in a direction in opposition to said fluid pressure whereby to connect said one side of said piston to drain, an abutment carried by said valve engaging one end of said spring, and an abutment movable with said piston engaging the other end of said spring whereby a constant spring compression is maintained.

2. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing and a cooperating cylinder, said cylinder being fixed to said casing, passage means connecting said casing with said source, a drain, a valve including a fluid controlling land movable relative to said casing having one end exposed to pressure from said connecting means, the pressure urging said valve and land in a direction to connect one side of said piston with pressure from said source, a spring urging said valve and land in a direction in opposition to said fluid pressure to connect said piston with said drain including a drilled passage within said valve and extending in the direction of motion of said valve, a first abutment carried by said valve engaging one end of said spring, and a second abutment movable with said piston engaging the other end of said spring whereby a constant spring compression is maintained.

3. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing and a cooperating cylinder, said cylinder being fixed to said casing, passage means connecting said casing with said source, a drain, a valve including a fluid controlling land movable relative to said casing having one end exposed to pressure from said connecting means, the pressure urging said valve and land in a direction to connect one side of said piston with pressure from said source, a spring urging said valve and land in a direction in opposition to said fluid pressure to connect said piston with said drain including a drilled passage within said valve, an abutment carried by said valve engaging one end of said spring, an abutment movable with said piston engaging the other end of said spring whereby a constant spring compression is maintained, a liquid chamber, and a disc-like member fixed to said valve and disposed in said chamber for damping movement of said valve.

4. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing, a cylinder cooperating with said piston and fixed to said casing, passage means connecting said casing with said source, a drain, a valve movable coaxially with and relative to said piston and casing, said valve having one end exposed to pressure from said con necting means, said pressure urging said valve in a direction to expose an operative side of said piston to the pressure from said source, an abutment carried by said one side of said valve, a sleeve surrounding said valve in radially spaced relation and movable with said piston, said sleeve including an abutment in axially spaced relation with said first mentioned abutment, and a spring located between said abutments and urging them apart so that said spring urges said valve in a direction opposing the pressure from said source, thereby to connect an operative side of said piston to said drain.

.5. A fluid motor, a source of fluid under pressure, a

control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing, a cylinder cooperating with said piston and fixed to said casing, passage means connecting said casing with said source, a drain, a valve movable coaxially with and relative to said piston and easing, said valve having one end exposed to pressure from said passage means, said pressure urging said valve in a direction to expose one operative sideof said piston to the pressure from said source, an abutment carried by said one side of said valve, a sleeve surrounding said valve in radially spaced relation and movable with said piston, said sleeve including an abutment in axially spaced relation with said first mentioned abutment, and a spring located between said abutments and urging them apart so that said spring urges said valve in a direction opposing the pressure from said source thereby to connect the other operative side of said piston to said pressure when said pressure reaches a predetermined value.

6. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing, a cylinder cooperating with said piston and fixed to said casing, passage means connecting said casing with said source, a drain, a valve movable coaxially'with and relative to said piston and casing, said valve having one end exposed to pressure from said passage means and urging said valve in a direction to expose an operative side of said piston, the other end of said valve being exposed to pressure from said drain, an abutment carried by said one side of said valve, a sleeve surrounding said valve in radially spaced relation and movable with said piston, said sleeve including an abutment in axially spaced relation with said first mentioned abutment, and a spring located between said abutments and urging them apart so that said spring urges said valve in a direction to aid the force of the drain pressure and oppose the force of the pressure from said source thereby to connect an operative side of said piston to said drain.

7. A fluid motor, a source of fluid under pressure, a control for said motor comprising a casing housing said motor, said motor including a piston movable relative to said casing and a cooperating cylinder, said cylinder being fixed to said casing, passage means connecting said casing with said source, a drain, a valve movable relative to said casing having one end exposed to fluid pressure from said passage means and urging said valve in a direction to connect one side of said piston with pressure from said source, a spring urging said valve in a direction in opposition to said fluid pressure, an abutment carried by said valve engaging one end of said spring, a sleeve surrounding said valve movable with said piston, and engageable with the other end of said spring, said sleeve being adapted for removal from the control whereby the spring compression may vary with changes in position of said piston.

References Cited in the file of this patent UNITED STATES PATENTS 840,876 Steedman Jan. 8, 1907 1,600,376 Trotter Sept. 21, 1926 1,601,009 Trotter Sept. 28, 1926 1,732,813 Kasley Oct. 22, 1929 2,163,479 Boddy June 20, 1939 2,338,021 Bennett Dec. 28, 1943 2,376,671 Dodson May 22, 1945 2,411,748 Kelley Nov. .26, 1946 2,689,527 Emerson Sept. 21, 1954 2,754,806 Funston July 17, 1956 FOREIGN PATENTS 850,534 France Dec. 19, 1939 885,907 France Sept. 29, 1943 400,057 Italy Nov. 24, 1942 

